Pressed work and manufacturing method thereof

ABSTRACT

A rolled steel plate as a raw material is press-formed into a pressed work provided with a boss section, and the work is fitted to a shaft by press-fitting of the shaft into the boss section. Rolling flow of internal metallographic layers in the boss section is curved like a letter S. Moreover, a manufacturing method of such a pressed work comprises: a primary-boss forming process during which a primary boss having a hole section and a protruding section protruding from the periphery of the hole section at a position corresponding to the boss section on a plane-like raw material is formed; and a boss-section forming process during which the protruding section is pressed and deformed in the protruding length direction to form the boss section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pressed work and a manufacturing method thereof, and, specifically, to a pressed work and a manufacturing method thereof, wherein a rolled steel plate as a raw material is press-formed into the pressed work with a configuration in which a boss section is provided, and the work is fitted to a shaft by press-fitting of the shaft into the above-described boss section according the method.

2. Description of the Related Art

There are various kinds of articles as a pressed work which is obtained by press-forming of a plane-like material, a bar-like one and the like. For example, there is a pressed work 20 which has a main body 21 with a disk-like shape, and a boss section 22 which is protruding from the one side of the main body 21, as shown in FIG. 3, wherein the boss section 22 is fitted to a shaft J of a correct device K by press-fitting of the shaft J into the boss section 22. And, the boss section 22 of such a pressed work 20 has been formed by bending of a material, using press-forming. Here, the press-forming is a forming method by which plastic deformation of a raw material is executed, and the forming method includes forming by forging in a broad sense.

Incidentally, a rolled steel plate has been generally used as a raw material of the pressed work 20. Here, the rolled steel plate has an internal metal structure in which metallographic layers are laminated in the thickness direction, and, at the same time, the metallographic layers uniformly flow in the surface direction of the rolled steel plate. Moreover, the flowing state of the metallographic layers can be observed as “rolling flow” by enlarging the section with a microscope.

Moreover, the raw material of the above-described conventional pressed work 20 has been simply formed by bending in such a way that the boss section 22 has approximately the same thickness as that of the raw material as shown in FIG. 4, and a rolling flow F has been a state that the internal metallographic layers are uniformly flowing in the bending direction.

Generally, the contents of the above-described prior art have been well known, but the present applicant has not found documents in which the contents are described.

As described above, the pressed work is fitted to the shaft by press-fitting of the shaft into the boss section, and the rolling flow has a state that the metallographic layers in the boss section are uniformly flowing in the bending direction, there has been a problem that the shaft is caused to rattle in the boss section, and, in some cases, the pressed work slips off from the shaft because the rigidity for a stress in the radial direction is low, and the diameter in the boss section is expanded after the boss section is fitted to the shaft.

This invention has been made, considering the above circumstances, and the object of the invention is to provide a pressed work and a manufacturing method thereof, by which a state that a shaft is firmly press-fitted into a boss section can be preferably maintained.

SUMMARY OF THE INVENTION

According to the present invention, main means which achieves the above-described object is: “a pressed work into which a rolled steel plate as a raw material is press-formed, and which is provided with a boss section, and is fitted to a shaft by press-fitting said shaft into said boss section, wherein rolling flow of internal metallographic layers in said boss section is curved like a letter S”.

According to the pressed work with the above-described configuration, the rigidity for a stress in the radial direction is improved, because the rolling flow of internal metallographic layers in said boss section is curved like a letter S. Accordingly, the boss section is not deformed easily in the radial direction even after the shaft is press-fitted into the boss section.

Accordingly, a state that the shaft is firmly press-fitted into the boss section can be preferably maintained according to the pressed work with the above-described configuration.

Additionally, the following method is proposed: “a manufacturing method of a pressed work into which a rolled steel plate as a raw material is press-formed, and which is provided with a boss section, and is fitted to a shaft by press-fitting said shaft into said boss section, said method comprising: a primary-boss forming process during which a primary boss having a hole section and a protruding section protruding from the periphery of said hole section at a position corresponding to said boss section on a plane-like raw material is formed; and a boss-section forming process during which said protruding section is pressed and deformed in the protruding length direction to form said boss section”.

In the above-described manufacturing method, the primary boss will be crushed in the length direction, that is, in the axial direction during the boss-section forming process because the primary boss, which has been formed during the primary-boss forming process and is provided with the hole section and the protruding section, is pressed and deformed in the direction of the protruding length of the protruding section during the boss-section forming process to form the boss section with the desired length. Therefore, when the boss section with the desired length is formed from the primary boss, the flow of the internal metallographic layers is changed by crushing to the rolling flow which is curved like a S character even in a state that the internal metallographic layers flow in the primary boss according to the rolling flow which is uniform.

Accordingly, the pressed work can surely be manufactured according to the manufacturing method with the above-described configuration, wherein, according to the pressed work, the boss section in which the rolling flow of the internal metallographic layers is curved like a letter S can be adequately formed, and the state that the shaft is firmly press-fitted into the boss section can be preferably maintained.

The above-described means also may be as follows: “the manufacturing method of a pressed work, comprising, as a preliminary process for said primary-boss forming process, a swelled-section forming process during which a plane-like raw material is swelled to form a swelled section at a position corresponding to said boss section, wherein during said primary-boss forming process, the central part of said swelled section is punched to form said primary boss provided with said hole section and said protruding section”.

In order to realize the boss section in which the rolling flow of the internal metallographic layers is curved like a letter S, it is required that a sufficient length is secured for the protruding length of the protruding section in the primary boss, and that the protruding is greatly pressed and deformed. Here, it is difficult to greatly protrude the protruding section, and to secure the sufficient protruding length for the protruding section when the hole section is formed on the plane-like raw material by punching, and, thereafter, the protruding section is formed by bending of the periphery of the hole section.

Then, according to the manufacturing method with the above-described configuration, a plane-like raw material is swelled and the swelled section is formed at a position corresponding to the boss section, and thereafter the central part of the swelled section is punched to form the primary boss. In such a manufacturing method, the protruding section with the sufficient protruding length can be formed, using the swelled section which has been greatly swelled, if the swelled section is greatly swelled before the hole section is formed during a preliminary step, because the protruding section is formed of the remaining portion of the swelled section in which the hole section is made by punching.

Therefore, according to the above-described manufacturing method, the primary boss can be greatly pressed and deformed to form the boss section with the desired length after forming the primary boss provided with the protruding section with the sufficient protruding length, and the boss section in which the rolling flow of the internal metallographic layers is curved like a letter S can be desirably formed.

As described above, the pressed work and the manufacturing method thereof can be provided according to the present invention, wherein the state that the shaft is firmly press-fitted into the boss section can be desirably maintained in the pressed work.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by the following detailed description of the preferred embodiments, when considered in connection with the accompanying drawings, in which

FIG. 1 is a cross-sectional view showing one example of a pressed work according to the present inventions;

FIG. 2(a) is a raw material in the process of a manufacturing method of the pressed work according to the present invention;

FIG. 2(b) is a large swelled section in the process of a manufacturing method of the pressed work according to the present invention;

FIG. 2(c) is a primary boss in the process of a manufacturing method of the pressed work according to the present invention;

FIG. 2(d) is a boss section in the process of a manufacturing method of the pressed work according to the present invention;

FIG. 3 is a perspective view showing one example of the pressed work; and

FIG. 4 is a cross-sectional view showing one example of a conventional pressed work.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a pressed work and a manufacturing method thereof according to the present invention will be explained in detail as one example, referring to drawings.

As shown in FIG. 1, a pressed work 10 includes a main body 11 with approximately a disk-like shape, and a boss section 12 which is protruding from the one side of the main body 11. Here, this pressed work 10 is fitted to a shaft J of a correct device K shaft J by press-fitting of the shaft J into the boss section 12 in a similar manner to that of a conventional article shown in FIG. 3.

Here, though such a pressed work 10 is fitted to extensively various kinds of devices K with a shaft J, an article which is fitted to a shaft section of a toothed pulley can be listed as one specific example, wherein the pulley winds a timing belt which transmits driving of a crank shaft in an engine to a camshaft. More specifically, the pressed work 10 is fitted to the toothed pulley in the toothed pulley by which there is caused a phase difference in rotation between a peripheral gear tooth section engaging the timing belt and a shaft section rotating the camshaft in order to control timing for opening and closing an intake and exhaust valve according to the number of engine rotations, and a wheel sensor for detecting the phase difference can be listed as one example, wherein the wheel sensor is fitted to the shaft section in order to detect the presence of a phase difference between the phase of the shaft section and that of the gear tooth section with a detector such as a proximity switch.

Incidentally, the boss section 12 is configured in such a way that the rolling flow F of the internal metallographic layers is curved like a letter S, though the pressed work 10 is obtained by press-forming rolled steel plate, more specifically, a steel plate meeting a steel-plate standard, “SAPH440”, of a Japanese Industrial Standard (JIS) G 3119 as a raw material into a configuration having the main body 11 with approximately a disk-like shape, and the boss section 12 which is protruding from the one side of the main body 11. This rolling flow F can be observed by enlarging the cross section of the boss section 12 by 400 times with the microscope.

Subsequently, a manufacturing method by which the pressed work 10 can be adequately manufactured will be explained in detail, referring to FIG. 2, wherein the rolling flow F of the internal metallographic layers in the boss section 12 in the pressed work 10 is curved like a letter S.

In the first place, a long length of a rolled steel plate, which is wound like a coil, is punched to form a raw material 1 with a disk-like shape, which will become the pressed work 10.:(a)

Subsequently, a central part of the raw material 1 is swelled to form a large swelled section 2, which is sufficiently swelled, at a position corresponding to the boss section 12 on the plane-like raw material 1.:(b)

Here, when the swelled section 2 is gradually made larger through a plurality of steps before the final swelled section 2 is formed, using the plane-like raw material 1, it is preferable in that neither breaking nor cracks are caused on the raw material 1. Moreover, it is preferable that the swelled section 2 is formed step by step in such a way that the geometry is gradually changed from a state, in which the diameter is large and the swelled amount is small, to another state, in which the diameter is small and the swelled amount is large. Thus, the central part of the raw material 1 can rise and the swelled section 2 which is greatly swelled can be finally formed.

Subsequently, the central part of the swelled section 2 is punched to form a primary boss 5 provided with a hole section 3 and a protruding section 4 protruding from the periphery of the hole section 3.:(c) Here, the protruding section 4 has an sufficient protruding length, because the protruding section 4 is formed of the remaining part of the above-described swelled section 2 after the hole section 3 is made.

Finally, the protruding section 4 of the primary boss 5 is pressed and deformed in the protruding length direction to form the boss section 12 which is protruding from one side of the main body 11 with approximately a disk-like shape by a desired protruding length.:(d) In other words, the primary boss 5 is crushed in the axial direction in such a way that the protruding length from the main body 11 is reduced to shorter by 10% through 50% than that of the primary boss 5 to form the boss section 12 with the desired length. Thereby, the boss section 12 in which the flow F of the internal metallographic layers is curved like a letter S is formed.

Here, the radial-direction rigidity of the boss section 12 is improved in comparison with that of a conventional one in this example, because the thickness of the boss section 12 is formed to be thicker than that of the raw material 1. Here, plastic deformation of the primary boss 5 is executed during a boss-section forming process, following both molds of a lower mold (die) at the lower side and an upper mold (punch) at the upper side to form the boss section 12. Moreover, plastic deformation is desirably executed to make the section 12 thick, following the molds, because the primary boss 5 supplies a sufficient amount of the raw material.

Incidentally, breaking and cracks are easily caused in a material at bending with a small curvature R. Accordingly, a sufficient effective length for contact with the shaft J cannot be secured, because the boss section 22 of the conventional pressed work 20 shown in FIG. 4 is formed by bending and a ratio of the R of the inner surface of the boss section to the thickness of the raw material is required to be set at a large value, for example, 1.5 or more. Thereby, there has been a problem that the shaft J is easily caused to rattle in the conventional pressed work 20 under a state that the work 20 is fitted to the shaft J.

On the other hand, as the boss section 12 is formed by pressing and deforming the primary boss 5 in this example, a ratio of the R of the inner surface (a part shown by an arrow B in FIG. 2(d)) of the boss section 12 to the thickness of the raw material 1 can be set at a small value, for example, 0.5 through 1.0 at pressing and deforming (crushing process) during the boss-section forming process, even though when the primary boss 5 is formed mainly by bending, the ratio of the R of the inner surface (a part shown by an arrow A in FIG. 2(c)) of the boss section 12 to the thickness of the raw material 1 is required to be set at a large value, for example, 1.5 or more. Accordingly, the effective length sufficient for contact with the shaft J can be secured, and the shaft J can be configured to hardly rattle in the boss section under a state that the boss section is fitted to the shaft J.

Especially, the geometry of the boss section 12 has a shape of a truncated cone in this example. Accordingly, the boss section with a sufficient thickness can be formed in such a way that the inner surface of the boss section has a small R, because the thickness at the end of the protruding side in the primary boss 5 is gathered to the other side in opposition to the protruding side, and is filled to a void space of the lower mold. Moreover, the radial-direction rigidity of the boss section 12 can be improved because the geometry of the boss section 12 can be configured to be a shape of a truncated cone to prevent stress concentration between the main body 11 and the boss section 12.

Though the pressed work and the method thereof according to the present invention has been explained as one example as described above, the pressed work according to the present invention is not limited to the above-described example. Actually, any boss section with a configuration in which a rolling flow of internal metallographic layers is curved like a letter S may be applied. For example, the configuration is not limited to that in which the boss section is protruding in a shape of a truncated cone, but there may also be applied another configuration in which the boss section is protruding in a shape of a cylinder, or further another configuration in which the thickness of the boss section is not thicker than, but is approximately the same as, that of the raw material.

Moreover, the pressed work with a configuration in which the rolling flow of the internal metallographic layers is curved like a letter S can be manufactured not only by the above-described manufacturing method, but also by another manufacturing method. For example, there can be applied various kinds of manufacturing methods, such as a method by which a part of a plane-like raw material is curved like a wave beforehand, wherein the part is corresponding to a boss section, and, thereafter, the part may be press-formed to obtain a boss section with a desired geometry, or another method by which the internal metallographic layers are deformed by heating.

It is readily apparent that the above-described also has the advantages of wide commercial utility. It should be understood that the specific form of the invention hereinabove described is intended to be representative only, as certain modifications within the scope of these teachings will be apparent to those skilled in the art. Accordingly, reference should be made to the following claims in determining the full scope of the invention. 

1. A pressed work into which a rolled steel plate as a raw material is press-formed, and which is provided with a boss section, and is fitted to a shaft by press-fitting said shaft into said boss section, wherein rolling flow of internal metallographic layers in said boss section is curved like a letter S.
 2. A manufacturing method of a pressed work into which a rolled steel plate as a raw material is press-formed, and which is provided with a boss section, and is fitted to a shaft by press-fitting said shaft into said boss section, said method comprising: a primary-boss forming process during which a primary boss having a hole section and a protruding section protruding from the periphery of said hole section at a position corresponding to said boss section on a plane-like raw material is formed; and a boss-section forming process during which said protruding section is pressed and deformed in the protruding length direction to form said boss section.
 3. The manufacturing method of a pressed work according to claim 2, comprising, as a preliminary process for said primary-boss forming process, a swelled-section forming process during which a plane-like raw material is swelled to form a swelled section at a position corresponding to said boss section, wherein during said primary-boss forming process, the central part of said swelled section is punched to form said primary boss provided with said hole section and said protruding section. 